1. Field of the Invention
The invention relates to conveyors with endless belts and, more particularly, to conveyors with low friction, positive drive belts capable of forming a trough to retain conveyed items on the belt.
2. Description of the Related Art
Conveyors with friction-driven flat belts are known systems for moving items from one location to another. A tensioned, endless belt extends between a drive pulley and a tail piece (typically a pulley or a fixed bar), whereby friction between the drive pulley and the belt enables transfer of torque from the former to the latter to thereby induce movement of the belt. Because tension on the belt is required to maintain the requisite friction for moving the belt, this type of conveyor does not perform well in environments where the tension and friction can be compromised. For example, in the food industry, introduction of grease and effluents from food products can result in a loss of friction and thereby detrimentally affect the performance of the conveyor.
Another type of conveyor comprises a direct or positive drive modular belt. In this type of conveyor, a modular belt formed of a plurality of interlocking links extends between a drive pulley and an idler pulley and comprises a plurality of teeth that engage corresponding sheaves on the drive pulley. Interaction between the teeth and sheaves transfers torque to the belt. As a result, the conveyor does not rely on friction for moving the belt, and the liquids associated with food handling do not affect performance in the manner described above for friction-driven belts. However, other problems arise when using low tension, direct drive modular belts in the food industry, most notably related to hygiene and cleanliness. For example, fluids and debris can become lodged in the joints of the interconnecting links, and are difficult to sanitarily remove.
Conveyors with a low friction, positive drive belt 100 having a flat surface 102 on one side and teeth 104 on the other side, as illustrated in FIG. 1, overcome the problems associated with the friction-driven flat belts and the modular belts. The seamless flat surface 102 is easy to clean, while the teeth 104 engage sheaves 106 on a drive sprocket 108 to transfer torque to the belt 100 without requiring friction between the belt 100 and the drive sprocket 108 or tension in the belt 100. Such a conveyor is disclosed in U.S. Pat. No. 7,850,562 to DeGroot, which is incorporated herein by reference in its entirety.
In the food handling industry, one problem associated with conveyors is retaining the conveyed item on the belt. Some items tend to migrate to the edges of the belt and, if not restrained, can fall off the belt. For conveyors with modular belts, one solution has been to provide side rails, but the items can become caught between the belt and the side rails. Alternatively, friction-driven belts can automatically form a trough when under sufficient tension, and the items naturally reside in the trough. Troughs are effective for alleviating the migration problem, but they do not automatically form in low friction, untensioned, positive drive belts.